Dentrification and oxygen consumption in bottom sediments: factors influencing rates of the processes

Rates of denitrification and oxygen consumption were measured in the sediment of four reservoirs in south-eastern Poland using an in situ chamber method. The in situ denitrification rate was calculated from the total N(2) flux from sediment, and the rate of oxygen consumption from the differences as a function of time in dissolved oxygen concentration in overlying water enclosed within in situ chambers. Denitrification rates for all the investigated lakes reached 1100 mumol N(2) m(-2) h(-1), and were similar to values reported for eutrophic reservoirs. The rate of oxygen consumption ranged from about 141 to 1890 mumol O(2) m(-2) h(-1). The factors influencing the rate of dentrification and oxygen consumption in bottom sediment such as light, temperature, nitrate and dissolved oxygen concentrations, pH in overlying water and available organic matter in the sediment were investigated. Dentrification rates were enhanced under natural light conditions. Temporal variations in dentrification rate and oxygen consumption appeared to be dominated by temperature. The rates of both processes were greater at 23 degreesC compared to 12 degreesC. The higher the concentration of nitrate in overlying water and organic matter in sediment, the greater the rate of dentrification. Orgenic matter concentration did not influence the oxygen consumption rate. Production of nitrous oxide, as the intermediate product of denitrification, was not observed, possibly due to the pH of overlying water (>7.3). A correlation between denitrification rate and oxygen consumption rate was found.